The invention relates to a spring-loaded oil overflow valve for diaphragm compressors.
Diaphragm compressors operate similarly to normal piston compressors, but with a separating diaphragm between the gas side and the oil side. The oil side is formed by the usual piston-cylinder unit, whose working and dead volumes are filled with oil. On the gas side are gas suction and pressure valves. The volume displaced by the oscillating movement of the piston is transmitted to the diaphragm, which then on its gas side causes the intake, compression and exhaust of the gases. Since the oil pressure during the entire reciprocating movement corresponds to the course of the suction and compression pressure on the gas side, one can here also talk in terms of the operating mode of a piston compressor.
A small difference from piston compressors exists however in that in the case of diaphragm compressors a secondary oil circuit must be installed to allow compensation for the leakage of oil. For this purpose a compensation pump, driven by an eccentric on the crank shaft is used. This in synchronism with each piston stroke injects a small amount of oil into the oil space of the compressor.
This amount must theoretically be exactly as large as the leakage at the compressor piston. Since this cannot be technically realized, always an injected amount of oil is used which is larger than the leakage. This in turn has the result that with each stroke of the compressor piston somewhat too much oil is contained in the oil space, which then at the forward dead point of the diaphragm                (that is, engaging the cover), leads to an uncontrollable increase in oil pressure. To prevent this, it is further necessary that an oil overflow valve be used, which limits the oil pressure at the forward dead point of the piston to a value which is slightly above the maximum pressure of the gas.        
The spring-loaded oil overflow valve with a valve seat and a sealing ball in the seat works as a safety valve and only allows the discharge of a quantity of oil that is actually too much for that delivered from the compensation pump to the oil space. This quantity, which is discharged with each stroke, is on the one hand dependent upon the opening characteristics of the oil overflow valve, that is, the configuration of the seat member and the elements responsible for the spring characteristic, and, on the other hand, the energy content of the oil space (pressure×volume) which has a strong influence on the corresponding behavior of the oil overflow valve. The latter leads to undesirable increases in the opening time of the oil overflow valve such that more oil is discharged than introduced by the compensation pump. This has the result that after many pumping strokes the diaphragm is no longer driven to its forward dead point. Consequently, not all of the compressed gas is discharged which is accompanied by a rapid decrease in the suction power.
In DE 10,056,568 the restriction apparatus arranged in the supply line for the oil overflow valve leads to a faster closing time by means of the associated pressure drop before the oil overflow valve; however, with this an additional valve control is necessary.